Kaikōura earthquake a one in 5000-10,000 year event

Wednesday, 4 July 2018

A special edition of the Bulletin of the Seismological Society of America focuses on Kaikōura quake. (Video first published July 2018)

The 2016 Kaikōura earthquake was so complex, another similar event isn't expected to happen again for 5000 to 10,000 years.

The magnitude-7.8 quake is now the subject of its own special issue of the Bulletin of the Seismological Society of America. The issue, published this week, contains 21 articles about the Kaikōura event.

One of the papers has 47 co-authors, led by GNS Science earthquake geologist Nicola Litchfield. It noted the two dozen faults involved in the quake had rupture intervals of between 300 and 10,000 years.

The 2016 quake was 'a relatively rare' event, they said, and estimated a similar event with the fault intervals coinciding happened every 5000 to 10,000 years.

**READ MORE:

The Kaikōura earthquake left great scars across the landscape.

* Before and after the Kaikoura quake: images show colossal damage

* New quake 'lake' now a popular tourist spot

Geologists map one of the many surface ruptures in the November 2016 Kaikōura earthquake.

* Kaikoura earthquake ruptured 21 faults - that's possibly a world record

* The Road: SH1 cut off by the 7.8 quake**

Damage to State Highway 1, near Kaikōura.

The rupture began near Waiau in North Canterbury and travelled northeast about 2km a second. It ended up off Cape Campbell in Marlborough, covering 174km in about 74 seconds, GNS said in a statement about the special Kaikōura issue.

The quake triggered tens of thousands of landslides, and caused the closure of a section of State Highway 1 for more than a year.

An example of the energy unleashed in the Kekerengu Fault rupture.

The southwest to northeast direction of the rupture strongly focused seismic energy toward the north.

An unusual feature of the quake was the distance the rupture jumped between faults. The fault step-overs of up to 22km had not been seen anywhere in the world.

The Litchfield-led article showed about two-thirds of the earthquake's energy was released on the 24 surface-rupturing faults. The remaining third was on the underlying Hikurangi subduction interface - the boundary where the Pacific and Australian tectonic plates meet.

The largest horizontal movement was 12 metres on the Kēkerengū Fault, while the largest vertical movement, or uplift, was 9m on the Papatea Fault. Along 110km of coastline, vertical movement ranged from subsidence of 2.5m to uplift of 6.5m.

There was also a small tsunami and tens of thousands of landslides over an area of about 10,000 square kilometres.

Several factors were thought likely to have contributed to the large number of faults involved in the quake.

They were the presence of the interface between the Pacific and Australian plates, physical linkages between faults, the rupture of geologically immature faults in the south, and the inherited geological structure.